Thanks for getting in touch.
So first of all, bearing mind that the results you get from the W3C HTML validator are not necessarily real problems (although some are). Often your page will run OK with some validation errors present, although you should try to fix any that you can.
It is still a useful guide however, which can help in finding errors.
In this case, your first error is complaining that the “|” character us being used in the URL inside the Google Fonts
<link> element, and that isn’t allowed. Well, this is the way Google decide to write their code. It’s invalid, but it works.
For the second error, it says you have an element
<dev> on your page, which isn’t allowed as a direct child of
<header>. I’m assuming that this is a typo, and you meant to write
<div>? I reckon that shold clear up that error.